1. Field of the Invention
The present invention relates to an ink jet recording apparatus for performing recording by ejecting ink from recording means onto a recording medium and, more particularly, to an ink jet recording apparatus having an improved cleaning member for cleaning an ink ejecting surface of the recording means.
2. Description of the Related Art
Recording apparatuses performing the functions of, for example, printers, copying machines or facsimiles, and recording apparatuses used as output apparatuses of work stations and combined apparatuses, such as computers or word processors, are constructed so as to record images (including characters, symbols, etc.) onto recording media such as sheets of paper, thin plastic sheets (for example, plastic sheets for an overhead projector and textiles). Such recording apparatuses can be divided into several groups according to their printing methods: ink jet recorders, wire dot recorders, thermosensitive recorders, thermal transfer recorders, laser beam printers, etc.
Further, such recording apparatuses can be characterized according to the scanning methods they use. A serial-type recording apparatus performs recording by scanning a recording medium in substantially perpendicular directions, that is, a main scanning direction and a sub-scanning direction (the conveying direction of the recording medium). When the recording medium is set in a predetermined recording position, the recording apparatus moves a carriage carrying recording means (a recording head) along a line across the recording medium, that is, in the main scanning direction. After one line of an image, characters or the like, is thus recorded, the apparatus conveys the recording medium a predetermined amount in the sub-scanning direction to enable recording of the next line of an image, characters or the like, that is, to enable performance of main scanning for the next line. The main and sub-scanning operations are thus repeated to record an image, characters or the like, in a desired area on the recording medium.
A line-type recording apparatus has an elongated recording head which substantially covers the entire width of a recording medium, and performs recording by conveying the recording medium only in the sub-scanning direction. When a recording medium is set in a predetermined recording position, the apparatus records an entire line of an image, characters or the like, and then conveys the recording medium a predetermined amount or a pitch to enable recording of the next line of an image, characters or the like. By continuously repeating this operation, the apparatus completes recording on the recording medium.
Ink jet recording, which performs recording by ejecting ink from recording means onto a recording medium, achieves various advantages. For example, it facilitates a reduction in the size of the recording means and an increase in recording resolution and speed. Further, it can perform recording on ordinary paper that requires no special treatment, thereby providing lower operating costs. Still further, ink jet recording avoids substantial impact with the recording medium, and therefore operates at a low noise. Further, it also facilitates color recording using a plurality of color inks.
Ink jet recording heads that use thermal energy to eject ink can be significantly reduced in size, because a recording head having highly-packed liquid passages and ejection orifices can be easily produced by using semiconductor device production techniques, such as etching, vapor deposition or sputtering, to form films of a top plate, liquid passage walls, electrodes, electrothermal converters, etc. on a substrate. Further, by utilizing integrated circuit techniques or micro-processing techniques, thermal ink jet recording heads having a substantial length or the shape of a panel (a two-dimensional head), and full multi-color recording means or high-density packaged recording means can be easily produced.
The ejection orifice surface of an ink jet recording head may collect undesired substances, such as ink, dust, paper dust or the like, during recording operations. To remove such undesired substances from the ejection orifice surface, an ink jet recording apparatus employs a cleaning mechanism for wiping the ejection orifice surface with a cleaning member, such as a rubber blade made of, for example, urethane.
However, because a conventional cleaning mechanism has a cleaning member formed in the shape of a plate or blade, it may not provide sufficient cleaning. For example, if the cleaning area of an ejection orifice surface is curved or sloped instead of flat, the contact angle between the cleaning member and the ejection orifice surface will vary as the cleaning member slides over the ejection orifice surface, which can prevent it from thoroughly cleaning the ejection orifice surface. Variations in the contact angle may also be caused by deterioration of the performance of the cleaning member, which is likely to result after a very long period of use.
FIG. 9 is a schematic perspective view of a scanning-type recording head and a cleaning member of a known ink jet recording apparatus. FIG. 10 illustrates the cleaning operation using the cleaning member shown in FIG. 9. As shown in FIGS. 9 and 10, a recording head 101 has an ejection orifice surface 102 facing recording medium. The ejection orifice surface 102 has a plurality of ejection orifices 103. A region 104 in which the ejection orifices 103 are arranged is recessed in relation to the other portions of the ejection orifice surface 102, in order to protect the ink ejecting portion and solve various technical problems. Undesired substances 105, such as ink droplets or paper dust, may land on the area around the ejection orifices 103.
A rubber blade cleaning member 106, such as a rubber blade, slidable on the ejection orifice surface 102, in the ejection orifice recess region 104, is provided at a position in the travel of the carriage (not shown in FIGS. 9 and 10) outside a recording region but within the operational range of the carriage. When the recording head 101 is moved from a position as shown in FIG. 9 in the direction indicated by arrow A, the rubber blade 106 slides over the ejection orifice surface 102, thus cleaning the ejection orifice surface 102 by removing undesired substances such as ink droplets or paper dust.
FIG. 10 is a schematic view of the recording head 101 and the rubber blade 106 contacting the recording head 101, viewed from the direction indicated by arrow B in FIG. 9. The rubber blade 106 is fastened to a holder 107. The holder 107 is movable substantially perpendicularly to the operational direction of the recording head 101 (arrow A) between a front position at which the rubber blade 106 can contact the recording head 101 and a rear position at which the rubber blade 106 will not interfere with the recording head 101. When the rubber blade 106 is at the front position and the recording head 101 is moved in the direction indicated by the arrow A, the rubber blade 106 slides over the ejection orifice recess region 104, thus performing a cleaning operation to remove the undesired substances 105 from the ejection orifice surface 102.
The conventional cleaning operation will be understood in more detail with reference to FIG. 10. While the rubber blade 106 slides on the ejection orifice surface 102 during the cleaning operation, the contact angle between the cleaning member 106 and the ejection orifice surface 102 varies. The contact angle is measured between the ejection orifice surface 102 and a tangent of the contact edge 108 of the rubber blade 106. When the rubber blade 106 is at a position (a) relative to the recording head 101, the contact angle between the cleaning member 106 and the ejection orifice surface 102 is .theta.a. When the rubber blade 106 enters the recess portion 104 as the recording head 101 is further moved in the direction indicated by arrow A, for example, when the rubber blade 106 is at a position (b), the contact angle becomes .theta.b. When the recording head 101 is further moved in the direction indicated by arrow A so that the rubber blade 106 enters an area in which the depth of the recess region 104 gradually decreases, for example, when the rubber blade 106 is at a position (c), the contact angle becomes .theta.c.
Because the ejection orifice surface 102 is curved, the contact angle .theta. between the rubber blade 106 and the ejection orifice surface 102 varies as the cleaning member 106 slides over the ejection orifice surface 102. In the case of the recording head as shown in FIGS. 9 and 10, the relation among the contact angles .theta.a, .theta.b and .theta.c is .theta.b&gt;.theta.a&gt;.theta.c. In general, when the contact angle .theta. between the rubber blade 106 and the ejection orifice surface 102 is within a certain range, high cleaning performance can be achieved. If the contact angle exceeds that range, the rubber blade 106 tends to draw ink out of the ejection orifices 103. If the contact angle becomes smaller than the range (for example, if the angle is .theta.c), the flat side surface of the rubber blade 106 can contact the ejection orifice surface 102, thereby failing to adequately clean the ejection orifice surface 102. Thus, if the contact angle .theta. between the rubber blade 106 and the ejection orifice surface 102 is out of an appropriate range, insufficient cleaning can result.
Therefore, to achieve sufficient cleaning, the contact angle .theta. between a cleaning member and the ejection orifice surface must be maintained at an optimal angle over substantially the entire ejection orifice surface. However, because the ejection orifice surface 102 in a conventional ink jet recording apparatus has a recess portion 104 with a curved surface, and because of long-term deterioration of such cleaning members, variation of the contact angle .theta. is generally inevitable. Therefore, in the conventional approach, a cleaning mechanism fails to perform uniform cleaning or cleaning performance deteriorates after a long period of use.
To eliminate this problem, a few methods can be conceived for reducing variations in the contact angle .theta., for example, adjusting the distance of the cleaning member holder 107 from the ejection orifice surface, or rotating the holder 107 in accordance with the shape or slope of the ejection orifice surface 102. However, control for such operations would be very complicated and difficult and mechanisms to accomplish them would be complex and bulky.